Improving heat transfer between sources of heat and associated heat removal hardware has become a critical limitation in many industries. One of those industries particularly affected is electronics, where miniaturization has significantly increased the heat flux required to maintain temperatures at low enough levels to prevent damage to electronic components. Common to many heat removal problems is the requirement to improve the thermal transfer between heat-generating components and heat removal hardware. Since the mating surfaces of these items are not perfectly flat, installation of a compliant material between them has become a common practice. The compliant material serves to fill the imperfections and gaps that are present, thereby removing air and substituting a material with higher thermal conductivity, resulting in improved heat transfer. These compliant thermal interface materials are commonly referred to as gap fillers.
Early technology made use of soft, thermally conductive, compliant gap fillers to improve thermal contact between materials. As a result, the thermal transfer improved between heat source components such as computer cpu's or gpu's, and the heat sink module used to remove heat. An improvement over this technology led to the introduction of materials that, when heated, soften or melt, allowing the material to re-arrange. If the mating surfaces are held together using pressure, the excess material is forced outside of the contact area, and the bond line becomes thinner, effectively reducing thermal resistance and allowing improved heat removal and lower temperature of the heat source. Such materials are generally referred to as phase change materials. Typical phase change materials used in the electronics industry consist of waxes and/or resins that are often filled with high thermal conductivity fillers to improve their thermal conductivity. An improvement over conventional phase change materials was developed recently through the use of low melting alloy phase change materials. An example of this is taught in applicants parent U.S. Pat. No. 6,372,997 the disclosure of which is incorporated herein by reference; describing, among other things, a three layer structure for placement between a heat source and heat sink, comprised of a low melting phase change alloy layer adhered on both sides to a copper core. Upon heating, the alloy melts on each mating surface to form a good thermal bond between the heat source and heat sink.
Miniaturization of electronic components and systems often presents difficulties in fitting heat removal systems into available space. In addition, in some situations both the heat source and the heat sink are in fixed positions with respect to the “system” but not with respect to each other hereinafter referred to as a “non-referenced die system” in which the distance between the heat sink and the heat source is a variable and can vary significantly (the “die” in this type of non-referenced system may represent an integrated circuit). In such situations it is impractical to use a thermal interface structure having a phase change layer on opposite sides of a metal core as taught in the aforementioned patent.